666 TEXT-BOOK OF PHYSIOLOGY 



any of the these nerve trunks is quite small in comparison with the efferent 

 fibers. In pathologic conditions of the organs the sensations to which they 

 give rise are frequently referred to areas of the cutaneous surface overlying 

 the lesion. 



THE FUNCTIONS OF THE AUTONOMIC NERVE SYSTEM 



The view according to which the sympathetic ganglia are to be regarded 

 as independent organs endowed with functions of their own and in nowise 

 directly dependent for their activities on the central nerve system is at the 

 present very largely discarded. Peripheral structures cease to exhibit 

 their characteristic functions after division of the spinal nerves in 

 connection with their related ganglia. This does not exclude the possibility 

 of the sympathetic cell-body, in virtue of the interchanges between it and 

 the blood and lymph by which it is surrounded, maintaining its own nutri- 

 tion and exerting possibly a favorable influence over the nutrition of periph- 

 eral tissues to which its post-ganglionic branches are distributed. 



From the number and fineness of the ultimate terminations of the 

 branches given off from the ganglion cells as well as their extensive distribu- 

 tion in all regions of the body, it has been suggested that they are distribu- 

 tors of the nerve impulses discharged in consequence of the stimulating influ- 

 ence of nerve impulses coming from the spinal cord, through the pre-gan- 

 glionic fibers. 



From the distribution of the post-ganglionic fibers, viz.: to the walls of 

 the blood-vessels, to the walls of the viscera, and to the epithelium of glands 

 and in some animals to the muscles of the hair follicles, it may be inferred 

 that the ganglia are associated with vaso-motor, viscero-motor, secreto-motor 

 and pilo-motor phenomena; and since the pre-ganglionic fibers are always 

 associated with the ganglia, anatomically and physiologically, it can be said 

 that they too are associated with the same series of phenomena. 



The functions of the autonomic nerve system, as determined from its 

 anatomic distribution and the results of experimental investigations, are to 

 augment or to inhibit the tonus of the blood-vessels including the heart, the 

 tonus of visceral walls and the activity of the epithelium of glands, and are, 

 therefore, the sum total of the functions of the vaso-motor, viscero-motor 

 and secreto-motor nerves, that is, the nerves which collectively constitute 

 this system. The extent to which these different modes of activity manifest 

 themselves in one or more regions of the body will depend to some extent 

 on the strength of the stimulus and the portion of the system subjected to 

 experiment, as will be apparent from the following statements. 



The Functions of the Mid-brain Autonomic Nerves. The functions 

 of the efferent pre-ganglionic nerve-fibers contained in the trunk of the oculo- 

 motor nerve, together with their post-ganglionic continuations (the ciliary 

 ganglion and its branches), are (a) To augment the tonus or degree of con- 

 traction of the sphincter pupilla or the sphincter iridis in accordance with in- 

 creasing intensities of light, and (b) to augment the tonus or degree of con- 

 traction of the ciliary muscle accompanying efforts of accommodation. The 

 result of the contraction of the sphincter pupillae is a diminution in the diame- 

 ter of the pupil and hence a diminution in the amount of light entering the 

 eye so that the perception of the image may be sharp and distinct. The 

 result of the contraction of the ciliary muscle is a relaxation of the suspensory 



